Hydraulic breaker

ABSTRACT

In a hydraulic breaker utilizing an oil pressure, mitigation of impact given to the machine body in order to prevent its damage as well as the damage of the rod portion which couples the piston integrally to the hammer head, and smoothening of the action of said hammer head, are both accomplished by the provision of: a bush mounted at the partition wall which defines the upper cylinder from the lower cylinder and provided with a conical recess for receiving a part of the oil which is used to control the motion of said piston; said piston having, at its end portion, a conical portion which can be loosely received in the conical recess of said bush; said rod portion having an intermediate portion whose diameter is smaller than that of the remaining portions thereof; and said hammer head slidably mounted in the lower cylinder and having a portion capable of sliding on the inner circumference of the lower cylinder, said portion having a length which is at least 1.3 times the inner diameter of said lower cylinder, said hammer head being mounted slidably in said lower cylinder via a liner provided on said hammer head.

United States Patent [1 1 Mori et al.

[451 Feb. 19, 1974 HYDRAULIC BREAKER [73] Assignee: Yutani Juko Kabushiki Kaisha,

Tokyo-to, Japan 22 Filed: Mar. 17,1972

21 Appl.No.:235,504

[30] Foreign Application Priority Data Mar. 27, 1971 Japan 46/18276 July 17, 1971 Japan 46/62955 July 19, 1971 Japan.... 46/63883 Aug. 12, 1971 Japan 46/72503 Aug. 12, 1971 Japan 46/72504 [52] U.S. Cl. 173/119 [51] Int. Cl 825d 9/18 [58] Field of Search 173/119, 120, 139

[5 6] References Cited UNITED STATES PATENTS 2,559,478 7/1951 Stone 173/119 2,661,928 12/1953 Topanelian, Jr..... 173/119 X 2,851,010 9/1958 Mori 173/119 X 2,917,025 12/1959 Dulaney.... 173/119 3,426,856 2/1969 Roll et al. 173/119 Primary ExaminerWerner H. Schroeder Attorney, Agent, or FirmCushman, Darby 8!. Cushman [57] ABSTRACT In a hydraulic breaker utilizing an oil pressure, mitigation of impact given to the machine body in order to prevent its damage as well as the damage of the rod portion which couples the piston integrally to the hammer head, and smoothening of the action of said hammer head, are both accomplished by the provision of: a bush mounted at the partition wall which defines the upper cylinder from the lower cylinder and provided with a conical recess for receiving a part of the oil which is used to control the motion of said piston; said piston having, at its end portion, a conical portion which can be loosely received in the conical recess of said bush; said rod portion having an intermediate portion whose diameter is smaller than that of the remaining portions thereof; and said hammer head slidably mounted in the lower cylinder and having a portion capable of sliding on the inner circumference of the lower cylinder, said portion having a length which is at least 1.3 times the inner diameter of said lower cylinder, said hammer head being mounted slidably in said lower cylinder via a liner provided on said hammer head.

11 Claims, 6 Drawing Figures PATENTEBFEBI 91974 SHEET 1 0F 3 PAIENTEUFEH I 9|974 SHEEI 2 OF 3 FIG .4

FIG. 3

PATENTEUFEB 3 91974 SHEET 3 BF 3' FIG.6

HYDRAULIC BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is concerned with a breaker, and more particularly, it pertains to a hydraulic breaker arranged to be operative so that, after the hammer has been lifted upwardly by utilizing an oil pressure, this hammer is quickly lowered downwarly by the expanding force of a spring, to thereby break an object.

2. Description of the prior art Breakers utilizing a gasoline engine or a compressed air as their driving power source, are known. However, these known breakers invariably produce very loud noises during use, and therefore they are not desirable. In order to eliminate or alleviate these offensive noises, there have been developed breakers utilizing a pressurized oil as the driving power source. In such a known hydraulic breaker, however, a cam mechanism which is driven, via a reducing gear, by a hydraulic motor is used to compress the springwhich is assigned to drive the hammer. However, such a mechanical mechanism as the reducing gear and the cam mechanism had the drawbacks of not only complicating the structure of the breaker as a whole, but also of giving rise to various problems in the aspects of manufacture and maintenance. In addition, the known hydraulic breaker of the aforesaid type had the drawbacks that, because of impact given to the breaker body at the time of an idle stroke, not only undesirable effects were imparted to the user, but also the breaker body as well as the constituent parts were easily damaged by the impact.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide a hydraulic breaker having a high percussive efficiency, which, as a whole, is constructed in a very compact size and which is designed so that no idle stroke is allowed to occur.

Another object of the present invention is to provide a hydraulic breaker operated by oil, which at the time the breaker is rendered to a state close to the idle stroke state due to the sudden decrease in the resistance of the object to be broken the percussion energy of the hammer is effectively absorbed in the body of the breaker to thereby mitigate the force of impact which is given to the respective parts of the breaker, whereby the breaker can be prevented from sustaining damages.

Still another object of the present invention is to provide a hydraulic breaker operated by oil, which is arranged so that no stresses are concentrated to a respective joints between a rod portion which couples the hammer head integrally to a hydraulically driven piston and said hammer head and said piston, whereby these joints are kept from being damaged by the stresses.

A further object of the present invention is to provide a hydraulic breaker operated by oil, which is arranged so that, during the motion of the hammer head, the latter will not make any transverse shaking relative to the direction of its motion, to thereby prevent the occurrence of breakage at the joint between the hammer head and the rod portion and also the development of burning, fusing or biting between the hammer head and the portions of the main body of the breaker due to frictions therebetween.

Other objects, features and attendant advantages of the present invention will become apparent by reading the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal view of an example of the breaker according to the present invention, partly illustrated in an explanatory fashion, showing the state of the breaker wherein the foremost end of the chisel which is inoperative is in contact with the object to be stricken thereby;

FIG. 2 is a longitudinal sectional view similar to FIG. 1 when the hammer has reached its uppermost positron; I

FIG. 3 is a longitudinal sectional view similar to FIG. 1 when the tip of the chisel is in a position away from the object to be stricken thereby and also the hammer is in its lowermost position;

FIG. 4 is a fragmentary enlarged view of FIG. 1, showing the detailed structure of the piston and its related portions;

FIG. 5 is a fragmentary longitudinal sectional view, showing the state in which the chisel is attached to the main body of the breaker in a manner different from that shown in FIG. 1; and

FIG. 6 is a fragmentary longitudinal sectional view, showing an example in which the structure of the valve member is somewhat different from that shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 through 4, reference numeral 1 represents the main body of the breaker, which is comprised of body portions 2, 3 and 4 which are united by fastening means such as bolts not shown. In the body portion 2 are formed a cylinder chamber 2a which comprises a small diameter region and a large diameter region, and alsov are formed oil channels 2b, 2c, 2d and 2e. Numeral 5 represents a valve member whose narrow diameter portion is liquid-tightly and slidably received in the small diameter region of the cylinder chamber 2a, and whose large diameter portion is similarly received in the large diameter region of said cylinder chamber 20. This valve member 5 is provided, at the end portion of its narrow diameter portion, with at least one notch 50 which can establish communication between the small diameter region and the large diameter region of the cylinder chamber 2a. The lower end of the larger diameter portion of the valve member 5 is formed in a frusto conical shape. The aforesaid notch 50 is useful in establishing communication between the small diameter region and the larger diameter region of the cylinder chamber 2a whenever the valve member 5 assumes its lowermost position shown in FIG. 3. Numeral 6 represents a piston which is liquid-tightly and slidably received in the large diameter region of the cylinder chamber 2a and has an oil chamber 6a which is opened and closed by the lower end of the valve member 5, at

lease one oil channel 6b communicating with said oil chamber 6a, and a small diameter portion 60 whose lowermost end is formed in a frusto-conical shape. The valve member 5 and the piston 6 divide the large diameter region of the cylinder chamber 20 into individual oil chambers 7, 8 and 9. One end of the oil channel 2b opens into the cylinder chamber 20 in such a manner that it is closed by the piston 6 only when this piston 6 is in its lowermost position shown in FIG. 3 and that it communicates with the oil chamber 9 whenever the piston 6 is in any one of the other positions. Also, both ends of the oil channel 20 open into the cylinder chamber 21: in such a way that, whenever the valve member 5 and the piston 6 are in their neutral positions (and which a chisel 22 is pressed on an object 25 in the valve member 5 and the piston 6 are somewhat pushed upwardly by the chisel 22) as shown in FIG. 1, they are both closed by said valve member 5 and the piston 6 respectively, and that when the valve member 5 and the piston 6 have reached their uppermost positions as shown in FIG. 2, they are communicated with the oil chambers 8 and 9 respectively, and further that, when both the valve member 5 and the piston 6 are in their lowermost positions as shown in FIG. 3, they are both closed again by the valve member 5 and the piston 6, respectively. One end of the oil channel 2d opens into the cylinder chamber 2a in such a fashion that it is closed by the piston 6 whenever this piston 6 has arrived at its upper position as shown in FIG. 2 and that it communicates with the oil chamber 8 whenever said piston 6 is in a position between its neutral position as shown in FIG. I and its lowermost position as shown in FIG.- '3. The other end of this oil channel 211 communicates with the oil channel 2e having one end opening into the cylinder chamber 2a to communicate with the oil chamber 7. The diameter of the small diameter region of the cylinder chamber 2a is preliminarily selected so that its cross sectional area is greater than the cross sectional area of the oil chamber 6a and is smaller than the effective pressure-receiving area formed at the bottom face of the large diameter portion of the piston 6. The symbol P represents an hydraulic (meaning oil pressure) pump. Numeral 10 represents an oil supply pipe having one end connected to the discharge side of said hydraulic pump P and the other end connected to the other end of the oil channel 212 via a known check valve l1 and a joint means not shown. This .check valve 11 acts in such a way that it opens only when the pressure of the oil discharged into the oil supply pipe l0'from the hydraulic pump P has gained a level above a certain value (normally in the order of 10 kg/cm to supply oil into the oil channel 2b. Numeral 12 represents an oil supply pipe which is branched from the oil supply pipe 10 upstream of the check valve 1 1 and is connected via a joint means not shown to the inlet end of the small diameter region of the cylinder chamber 2a. Numeral 13 represents an oil tank. Numeral 14 represents an oil supply pipe connecting said oil tank 13 to the suction side of the hydraulic pump P. Numeral 15 represents an oil supply pipe which connects the other end of the oil channel 2e to the oil tank 13. In the body portion 3 are formeda stepped recess 3a, a cylinder chamber 3b and a bore which establishes communication between said stepped recess 3a and the cylinder chamber 312. Numeral 16 represents a bush which is fixedly mounted in the stepped recess 3a and has a recess 16a consisting of a cylindrical portion 16a and a frusto-conically shaped portion 16a" to loosely receive the small diameter portion 6c of the piston 6 as shown clearly in FIG. 4. This bush 16 also has an opening 16b. Numeral l7 represents a rod which is inserted loosely in the bone 3c and is inserted liquid-tightly and slidably in the opening 16b via an O-ring 18 which, in turn, is mounted in the inner circumferential wall face of the opening 16b. This rod 17 has its upper end screwed to the small diameter portion 60 which is formed at the bottom portion of the piston 6, and has its lower end portion provided with a hammer head 17a which, in turn, is slidably received in the cylinder chamber 3b. Numeral 19 represents a pin firmly inserted in the joint portion of the piston 6 and the rod 17 in the diametrical direction thereof. This pin 19 serves to insure the firm coupling of these two members. The intermediate portion 17b of the rod 17 is formed so that its diameter is smaller than that of the remaining portions thereof. The hammer head 17a, on the other hand, is formed as being substantially hollow, and the length of that portion thereof which slides on the inner circumference of the cylinder chamber 3b is selected so that it is at least 1.3 times the diameter of the hammer head 17a. Furthermore, the lowermost end of this hammer head 17a is rounded. At least one line 20 is mounted on the external circumference of the hammer head 17a. Numeral 21 represents a coil spring inserted between the hammer head 17a and the upper wall of the cylinder chamber 3b for urging the rod 17 to move downwardly. The body portion 4 is provided with a bore 4a in which is slidably received the shank portion 22b of the chisel 22 which can be brought into contact with the lowermost end of the hammer head 17a and which has a flange 22a capable of being brought into contact with the lower end face of the body portion 4. On the upper face of the body portion 4 is mounted a supporting plate 23 having an opening for passing therethrough the shank portion 22b of the chisel 22. In the bore 4a of the body portion 4 is provided firmly a pin 24 having a part of its circumference exposed and projecting from the wall of this bore 4a. Also, in a part of the external circumference of the shank portion 22b of the chisel 22 is formed, in the lengthwise direction of the shank portion 22b, a notch 22b having a length of several centimeters. This notch 22b engages the pin .24. Accordingly, the chisel 22 is able to travel through the distance between the position shown in FIG. 1 and the position shown in FIG. 3. More specifically, in case the foremost end edge of the chisel 22 is positioned away from the object 25 which is to hit thereby, the descending movement of the chisel 22 due to the gravity is limited by the engagement of the pin 24 with the notch 22b. This limitation, in turn, determines the lowermost positions of both the piston 6 and the valve member 5.

In FIG. 5, there is shown an example of the manner in which the chisel 22 is attached to the body portion 4, in a way somewhat different from that shown in FIG. 1. In the instant example, however, the body portion 4 consists of a block 4A and a cover member 48 which are united together integrally by fastening means such as bolts. In the block 4A are formed an opening 4A and a chamber 4A". The shank portion 22b of the chisel 22 is passed through this opening 4A, and also the flange 22a is accommodated in the chamber 4A". In this chamber 4A is received a coil spring 26 which is loosely wound around the shank portion 22b. This coil spring 26 normally urges the chisel 22 downwardly. In this way, the range of movement of the chisel 22 is limited by the upper wall of the chamber 4A" and also by the cover member 48 which contacts the lower face of the flange 22a.

In the example shown in FIG. 6, the valve member 5 is hollow and this serves to substantially reduce the mass of the valve member 5 per se. Also, in lieu of providing a notch 5a at the upper end of the narrow diameter portion of the valve member 5 shown in the example of FIG. 1, the valve member 5 in the instant example of FIG. 6 is constructed in such a way that, when this valve member 5 has descended to its lowermost position, the narrow diameter portion of the valve member 5 exists completely from the lower end of the small diameter region of the cylinder chamber 2a, whereby this small diameter region of the cylinder chamber 2a is brought into communication with the oil chamber 7.

Description will next be directed to the action of the breaker embodying the present invention.

FIG. 1 shows the state in which the body 1 is urged against the object 25 which is to be struck by its chisel 22. In this state, however, the chisel 22 is in its lifted position, the pin 24 engaging the lower end of the notch 22b. In this state, the notch 50 of the valve member 5 is shutting off the communication between the small diameter region of the cylinder chamber 2a and the oil chamber 7, and the breaker is in the state of being ready for motion. Let us now assume that the hydraulic pump P is actuated so that a pressurized oil is forced from the oil tank 13 into the oil supply pipe 10. Whereupon, the pressurized oil will be supplied via the oil supply pipe 12 into the small diameter region of the cylinder chamber to apply a pressure onto the upper end of the narrow diameter portion of the valve member 5. At the same time therewith, the check valve 11 opens and the pressurized oil is fed into the oil chamber 9 via the oil channel 2b. Therefrom, the oil is passed into the oil chamber 6a via the oil channels 6b, applying a pressure onto the lower end of the valve member 5. Since the pressure-receiving area at the upper end of the narrow diameter portion of the valve member 5 is greater than the pressure-receiving area at the lower end of the valve member 5, the piston 6 is pressed by the valve member 5 However, since the pressurereceiving area at the upper end of the narrow diameter portion of the valve member 5 is smaller than the effective pressure-receiving area at the bottom face of the piston 6, the pressure oil acting on the bottom face of the piston 6 will cause the piston 6 and valve member 5 to move upwardly against the opposing forces of the spring 21 and the pressure oil acting on the upper end face of the small diameter portion of the valve member 5. When the piston 6 thus reaches its uppermost position shown in FIG. 2, the oil chambers 8 and 9 are rendered communicative via the oil channel 20, allowing the pressurized oil contained in the oil chamber 9 to flow into the oil chamber 8 to separate the piston 6 away from the valve member 5. As a result, the oil chamber 6a is opened, so that the pressurized oil contained in the oil chamber 9 quickly flows into the oil chamber 8 via the oil channel 6b and the oil chamber 6a to thereby apply a pressure onto the upper face of the piston 6. As a consequence, the piston 6, the rod 17 and the hammer head 17a make a quick descension, by virtue of the restoring force of the coil spring 21 and the oil pressure acting on the upper face of the piston 6. During this operation, the valve member 5 effects a delayed descension relative to the descension of the piston 6, while feeding back the oil contained in the oil chamber 8 into either the oil chamber 7 or the oil tank 13 via the oil channels 2d, 2e and the oil supply pipe 15 by virtue of the oil pressure acting upon the upper end of the narrow diameter portion of the valve member 5. Thus, the hammer head 17a will heavily strike the chisel 22 by the expanding force of the coil spring 21. As a consequence, a powerful impact is given to the object 25, which is thus broken.

As the piston 6, the rod 17 and hammer head 17a make a descension, the small diameter portion 60 of the piston 6 is received into the recess 16a of the bush 16. Therefore, the oil enclosed in this recess 16a is caused to flow out therefrom into the oil chamber 9 through a small gap D formed between the inner circumference of the cylindrical portion 16a of the bush 16 and th external circumference of the cylindrical portion 6c formed on the small diameter portion 60 of the piston 6, and during this flow of the oil, the latter applies a breaking action to the descending movement of the piston 6. Let us now assume that the resistance value of the oil as it is enclosed in the recess 16a is expressed as R, that the size of the aforesaid gap as D, the length of the overlapping portion of the two cylindrical portions 16a and 60 as L, and the proportional constant as K. Then, the resistance value R is expressed by KIA/D Accordingly, as the small diameter portion 6c of the piston 6 is received progressively into the recess 16a of the bush 16, the length L of the overlapping portion of the cylinrical portions 16a and 60' will increase. As a result, the resistance value will increase accordingly. More specifically, the aforesaid actions may be summarized as follows. As the piston 6 makes a descension progressively, the breaking force applied to this movement increases, resulting in an increase in the amount of absorption of the energy of motion of the hammer head 17a. Thus, at the time at which the lower end face of the hammer head 17a hits the supporting plate 23,

the small diameter portion 60 of the piston 6 is received deeply in the recess 16a of the bush 16, with the resistance value R reaching its maximum value. Accordingly, even if the hammer head 17a runs into the supporting plate 23, the impact which is sustained by the main body 1 will be quite small. It will be understood that even if the object 25 to be hit happens to be soft and brittle and easily breakable, there never occurs such an accident that the chisel 22 breaks the pin and plunges outside the body portion 4 or that the main body 1 is damaged by the impact.

In addition, as shown in the drawings, the intermediate portion l7b of the rod 17 is formed so that it has a reduced diameter relative to the end portions thereof, so as to give the entire rod 17 some flexibility and pliancy. Accordingly, when the hammer head 17a heavily hits the chisel 22, the stresses which are produced within the piston 6, the rod 17 and hammer head 17a as the reaction of this hitting is led to the vicinity of the intermediate portion 17b of the rod 17. As a consequence, when the hammer head 17a hits the chisel 22, the hammer head 17a and the lower portion of the rod 17 as well as the piston 6 and the upper portion of the rod 17 vibrate jointly, so that there takes place no concentration of the stresses onto the respective joint portions between the rod 17 and the piston 6 and between the rod 17 and the hammer head 17a. Thus, there occurs no breaking of these joint portions.

Furthermore, the hammer head 17a is formed as a substantially hollow member to minimize its weight and along with this, the area of sliding of the hammer head 17a and the cylinder chamber 3b is enlarged, and moreover two liners 20 are mounted on the external circumference of the hammer head 17a. Such arrangement contributes greatly to the smooth and light sliding movement of the hammer head 17a. Accordingly, the hammer head 17a will never cause transverse shaking. As a result, there will arise no breakage of the joint portion of the hammer head 17a and the rod 17. Not only that, but also it is possible to completely prevent the occurrence of burning, fusing and/or biting at surfaces due to friction between the sliding members. Experiments undertaken by the inventors showed that the greatest effectiveness was obtained when the length of that portion of the hammer head 170 which slide on the inner circumference of the cylinder chamber 3b was above 1.5 times the diameter of the hammer head 17a.

Furthermore, as shown in the drawings, the lowermost end of the hammer head 17a is rounded. Accordingly, the energy of motion of the hammer head 17a is transmitted effectively to the chisel 22, and thus the efficiency of hitting can be enhanced markedly. Not only that, but also there is the advantage that, when the hammer head 17a hits the chisel 22, the hammer head 170 will not cause any lateral shaking.

As stated above, after the hammer head 17a has hit the chisel 22, the valve member 5, the piston 6, the rod 17 and the chisel 22 will resume the state shown in FIG. 1. Therefore, throughout the period in which the hydraulic pump P is being actuated, the hammer head 17a will repeat its action of hitting the chisel 22. However, when the chisel 22 is struck repeatedly by the hammer head 17a, causing the object 25 to be eventually broken by this chisel 22 and as, accordingly, this object 25 ceases to be the object to be broken or when, likewise, the tip of the chisel 22 becomes positioned completely apart from the object 25, rendering the rod 17 to stay in its lowermost position as shown in FIG. 3 after having reached there, the oil channel 2b will be closed by the piston 6, and the notch a of the valve member 5 will establish communication between the small diameter region of the cylinder chamber 2a and the oil chamber 7. As a consequence, the oil which is forced to flow by the hydraulic pump P is passed through the oil supply pipes and 12, the smaller diameter region of the cylinder chamber 2a, the notch 5a, the oil chamber 7, the oil channel 2e and the oil supply pipe 15, and is fed back into the oil tank 13, so that the breaker is rendered inoperative. Thus, the so-called idle stroke can be prevented effectively.

The actions of those examples shown in FIGS. 5 and 6 are similar to those described of the example shown in FIG. 1, and therefore their explanation is omitted.

We claim:

1. A hydraulic breaker comprising a body having substantially a cylindrical shape; an upper cylinder chamber and a lower cylinder chamber both defined within said main body on its central axis; a chisel slidably received in the lowermost end portion of said body with a limited range of sliding movement; a rod member having at its lower end a hammer head slidably received in said lower cylinder chamber and capable of contacting the upper surface of said chisel, said rod member liquid-tightly and slidably passing through a partition wall provided between said upper cylinder chamber and said lower cylinder chamber and projecting into said upper cylinder chamber; a coil cpring loosely wound around said rod member for urging this rod member downwardly; a piston liquid-tightly and slidably received in said upper cylinder chamber and having, at its lower side, a small diameter portion coupled to said rod member and having, in its upper surface, an oil chamber and also at least an oil channel communicating with said oil chamber and opening to the upper cylinder chamber below its piston in the vicinity of said small diameter portion; a valve member liquid-tightly and slidably received in said upper cylinder chamber, and having, at its lower side, a frustoconical shaped portion capable of closing said oil chamber, and also having, at its upper side, a columnar portion liquid-tightly and slidably received in a diameter region of said upper cylinder chamber and having an effective pressure-receiving area larger than the cross sectional area of said oil chamber but smaller than the effective pressure-receiving area at the lower side of said piston; a first variable volume oil chamber defined above the columnar portion of said valve member in said upper cylinder chamber a second variable volume oil chamber defined between said valve member and said piston in said upper cylinder chamber; a third variable volume oil chamber defined below said piston in said upper cylinder chamber; a first oil channel arranged so as to be closed by said piston and arranged so as to communicate with said third oil chamber; a second oil channel arranged so as to be closed by said valve member and arranged so as to establish communication between said second and third oil chambers a third oil channel arranged so as to be closed by said piston and arranged so as to communicate with said second oil chamber; and a fourth oil channel communicating with said third oil channel and opening into said first oil chamber; said hydraulic breaker being so arranged that when the pressure oil is supplied into said third oil chamber via said first oil channel under the state in which said second oil channel is closed by said valve member and said piston, respectively, and in which said third oil channel communicates with said second oil chamber, said piston is upwardly moved together with said valve member by the oil pressure in said third oil chamber to compress said coil spring, and that when said second oil chamber is communicated with said third oil chamber via said second oil channel and said third oil channel is closed by said piston, said piston is quickly moved downwardly by the restoring force of said coil spring and the oil pressure applied on the upper surface of said piston to strike said chisel through said hammer head.

2. A hydraulic breaker according to claim 1, in which the columnar portion of said valve member has a notch so that, whenever said valve member is in its lowermost position, communication is established by this notch between the smaller diameter region of said upper cylinder chamber and said first oil chamber.

3. A hydraulic breaker according to claim 1, in which the columnar portion of said valve member is a hollow cylinder, and when said valve member is in its lowermost position, said columnar portion is allowed to exit completely from the small diameter region of said upper cylinder chamber.

4. A hydraulic breaker according to claim 1, in which the partition wall provided between said upper cylinder chamber and said lower cylinder chamber includes a bush having a recess for receiving the small diameter portion of said piston therein.

5. A hydraulic breaker according to claim 4, in which said recess comprises a cylindrical portion and a frustoconical portion, and said small diameter portion of said piston comprises a cylindrical portion and a frustoconical portion.

6. A hydraulic breaker according to claim 1, in which said first oil channel contains a check valve.

7. A hydraulic breaker according to claim 1, in which the intermediate portion of said rod member has a diameter smaller than the end portions of this rod member.

8. A hydraulic breaker according to claim 1, in which the longitudinal length of the slidable face portion of rounded. 

1. A hydraulic breaker comprising a body having substantially a cylindrical shape; an upper cylinder chamber and a lower cylinder chamber both defined within said main body on its central axis; a chisel slidably received in the lowermost end portion of said body with a limited range of sliding movement; a rod member having at its lower end a hammer head slidably received in said lower cylinder chamber and capable of contacting the upper surface of said chisel, said rod member liquid-tightly and slidably passing through a partition wall provided between said upper cylinder chamber and said lower cylinder chamber and projecting into said upper cylinder chamber; a coil cpring loosely wound around said rod member for urging this rod member downwardly; a piston liquid-tightly and slidably received in said upper cylinder chamber and having, at its lower side, a small diameter portion coupled to said rod member and having, in its upper surface, an oil chamber and also at least an oil channel communicating with said oil chamber and opening to the upper cylinder chamber below its piston in the vicinity of said small diameter portion; a valve member liquid-tightly and slidably received in said upper cylinder chamber, and having, at its lower side, a frusto-conical-shaped portion capable of closing said oil chamber, and also having, at its upper side, a columnar portion liquid-tightly and slidably received in a diameter region of said upper cylinder chamber and having an effective pressure-receiving area larger than the cross sectional area of said oil chamber but smaller than the effective pressure-receiving area at the lower side of said piston; a first variable volume oil chamber defined above the columnar portion of said valve member in said upper cylinder chamber a second variable volume oil chamber defined between said valve member and said piston in said upper cylinder chamber; a third variable volume oil chamber defined below said piston in said upper cylinder chamber; a first oil channel arranged so as to be closed by said piston and arranged so as to communicate with said third oil chamber; a second oil channel arranged so as to be closed by said valve member and arranged so as to establish communication between said second and third oil chambers a third oil channel arranged so as to be closed by said piston and arranged so as to communicate with said second oil chamber; and a fourth oil channel communicating with said third oil channel and opening into said first oil chamber; said hydraulic breaker being so arranged that when the pressure oil is supplied into said third oil chamber via said first oil channel under the state in which said second oil channel is closed by said valve member and said piston, respectively, and in which said third oil channel communicates with said second oil chamber, said piston is upwardly moved together with said valve member by the oil pressure in said third oil chamber to compress said coil spring, and that when said second oil chamber is communicated with said third oil chamber via said second oil channel and said third oil channel is closed by said piston, said piston is quickly moved downwardly by the restoring force of said coil spring and the oil pressure applied on the upper surface of said piston to strike said chisel through said hammer head.
 2. A hydraulic breaker according to claim 1, in which the columnar portion of said valve member has a notch so that, whenever said valve member is in its lowermost position, communication is established by this notch between the smaller diameter region of said upper cylinder chamber and said first oil chamber.
 3. A hydraulic breaker according to claim 1, in which the columnar portion of said valve member is a hollow cylinder, and when said valve member is in its lowermost position, said columnar portion is allowed to exit completely from the small diameter region of said upper cylinder chamber.
 4. A hydraulic breaker according to claim 1, in which the partition wall provided between said upper cylinder chamber and said lower cylinder chamber includes a bush having a recess for receiving the small diameter portion of said piston therein.
 5. A hydraulic breaker according to claim 4, in which said recess comprises a cylindrical portion and a frusto-conical portion, and said small diameter portion of said piston comprises a cylindrical portion and a frusto-conical portion.
 6. A hydraulic breaker according to claim 1, in which said first oil channel contains a check valve.
 7. A hydraulic breaker according to claim 1, in which the intermediate portion of said rod member has a diameter smaller than the end portions of this rod member.
 8. A hydraulic breaker according to claim 1, in which the longitudinal length of the slidable face portion of said hammer head is at least 1.3 times the diameter of this hammer head.
 9. A hydraulic breaker according to claim 1, in which the slidable face portion of said hammer head has at least one liner mounted thereon.
 10. A hydraulic breaker according to claim 1, in which said hammer head is a bottomed hollow cylindrical member.
 11. A hydraulic breaker according to claim 1, in which the lowermost end of said hammer head is rounded. 